Function Of Heat Treatment Temperature Research Articles

Enhanced absorption and emission of Y_3Al_5O_12:Ce^3+ thin layers prepared by epoxide-catalyzed sol-gel method

We have developed a method for fabricating thin layers of Ce3+ doped yttrium aluminium garnet, Y3Al5O12 (YAG:Ce) based on a sol-gel approach with propylene oxide as a gelation initiator. A single spin-coating process followed by a sequence of heat treatments allows the fabrication of polycrystalline YAG:Ce thin layers with a thickness of a few hundreds of nanometers. Surface morphology, crystallite size, and quantum efficiency are examined as a function of heat treatment temperature. The optical quality of the layer is further investigated by measuring the enhanced absorption of light coupled into the layer. We fabricate a three-layered slab waveguide system consisting of a fused silica glass substrate, a YAG:Ce layer and a SiO2 upper layer, and excite the system by illumination through a prism. The incident light couples to the fundamental waveguide mode in the YAG:Ce layer where it is eventually absorbed, resulting in an enhancement of absorption by a factor of 30. In correspondence, we observe a similar increase in emission intensity of photoluminescence caused by the enhanced absorption.

Effect of Heat-treated Temperature on the Carbon-supported Cobalt Pyridine Electrocatalysts for Oxygen Reduction

CoPy/C catalysts for the oxygen reduction reaction(ORR) were prepared with 40/60(mass ratio)(15%Co25%Py/C) using cobalt sulfate hepathydrate(CoSO4·7H2O) and pyridine(Py) as the Co and N precursors supported on Vulcan XC-72R followed by heat treatment in an inert atmosphere at different temperatures ranging from 600 ℃ to 900 ℃.The catalysts were characterized by TEM,XRD and SEM-EDS anlaysis.Their ORR activities as the function of heat treatment temperatures for catalyst synthesis were evaluated by cyclic voltammograms(CVs) and rotating disk electrode(RDE) measurements.The results show that high temperature treatment can greatly improve the ORR activity of CoPy/C catalyst,for which the catalyst synthesized at 800 ℃ exhibits the best ORR activity.The nanoparticles of the catalyst as-prepared,with a diameter of 17 nm,uniformly dispersed on Vulcan carbon(Vulcan XC-72R).XRD and EDS anlaysis indicate that the structure of CoPy/C is destroyed after high temperature pyrolysis,and changed as the different valence cobalt oxide and cobalt sulfide,which are with N and S as the active sites for ORR.In 3.0 mol/L KOH,15%Co25%Py/C(in O2) can produce the obvious ORR current,giving the onset potential at 0.026 V(vs.SCE) with a half-wave potential of-0.069 V.RDE results further reveal that 15%Co25%Py/C catalysts in 3.0 mol/L KOH solution catalyze the ORR via four-electron pathway,through which the molecular oxygen is directly reduced to H2O.

Agar-based heat-sensitive gel with linear thermal response over 65–80 °C

A nontoxic heat-sensitive gel containing 1.5 % (w/v) agar and 25 % (w/v) bovine serum albumin (BSA) was fabricated in this study. Optical density measurements with 808 nm near-infrared (NIR) laser indicated that, in spite of its BSA content, the current agar + BSA gel remained similar to agar only gel in terms of its optical response to NIR laser. The thermal response of the current agar + BSA gel to high temperatures was quantified using magnetic resonance imaging (MRI). According to the MRI measurements of T2 relaxation rate as a function of heating temperature, the current agar + BSA gel showed a linear response to heating temperatures between 65 and 80 °C, while it remained thermally stable at temperatures up to 80 °C. Therefore, the current agar + BSA gel can be used as thermal dosimeters or volumetric heat-sensitive gel phantoms in typical thermal therapy regime.

Synthesis, characterization and electrical properties of sol–gel derived 0.63Bi(Mg1/2Ti1/2)O3–0.37PbTiO3 high-Tc piezoelectric ceramics

The nano-scaled powders of a high Curie temperature piezoelectric system with a composition of 0.63Bi(Mg1/2Ti1/2)O3–0.37PbTiO3 (0.63BMT–0.37PT) have been synthesized via a citrate sol–gel method. The thermal decomposition process of the as-prepared xerogel was investigated through the thermo-gravitometry and differential scanning calorimetry. The lattice structure of the powders as the function of heat-treatment temperatures was explored by using X-ray diffraction, Fourier-transform infra-red and Raman spectra. The results indicated that the transparent gel could be obtained via the chelate reaction of citric acid with ethylene glycol and ethanolamine assist. Gels can be transformed into crystallite powders with a single-phase perovskite structure when heat-treated at 600 °C for 3 h, much lower than that of traditional solid-state reaction method. The sol–gel derived 0.63BMT–0.37PT ceramics sintered at 1020 °C exhibit excellent dielectric, ferroelectric and piezoelectric properties of Tc = 463 °C, ɛ33T=1208, tan δ = 0.063, Pr = 22.1 μC cm−2 and d33 = 230 pC N−1. Moreover, a small amount of Mn2+ doping could cause the reduced leakage current and slightly increased Tc values.

Nanocrystalline diamond coating on carbon fibers produced at different temperatures: Morphological, structural and electrochemical study

In this paper, the morphological, structural and electrochemical properties of nanocrystalline diamond (NCD) films grown on carbon fibers (CF) were investigated. The CF substrates were produced at three different heat treatment temperatures (HTT):1000, 1500 and 2000°C. The HTT variation promoted different organization indexes on the CF structures. Consequently, the NCD coating formation was strongly affected by the substrate HTT. The changes in the properties of the diamond films were discussed as a function of the film morphology evolution using CH4 flow rate of 0.25, 0.5 and 1.0sccm in the feed gas. The X-ray diffraction measurements for the CF and NCD/CF composites were determinant to characterize the crystallinity of the NCD films as a function of the CF HTT and of the CH4 addition. Based on the diffractograms, the Scherrer's equation was applied to the (111) NCD peak, resulting in grain size values varying from 11.0 to 5.0nm depending on the CH4 flow rate and on the CF HTT. The scanning electron microscopy images confirmed the deposition of a continuous NCD coating with high nucleation rate covering the whole CF, while their quality was analyzed by Raman spectroscopy measurements. The NCD grain agglomerates increased as a function of the increase in the CH4 flow rate from 0.25 to 1.0sccm, showing similar film morphology to that of the unfaceted diamond balls obtained by chemical vapor deposition. This behavior confirmed the expected tendency by decreasing the diamond quality with the CH4 addition, especially for the films grown on CF treated at 1500 and 2000°C. This performance was also corroborated by the cyclic voltammetry measurements concerning the electrode potential window and their responses in a redox couple.

Thermal Properties of 0.9CaMgSi2O6-0.1MgSiO3Glass-Ceramics

Dependencies of thermal properties on the crystallization behavior of 0.9CaMgSi 2 O 6 -0.1MgSiO 3 glass-ceramics were investigated as a function of heat-treatment temperature from 750℃ to 950℃. The crystallization behavior of the specimens depended on the heat-treatment temperature, which could be evaluated by differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis by the Rietveld-reference intensity ratio (RIR) combined procedure. With an increase of the heat-treatment temperature, the thermal conductivity and thermal diffusivity of the heat-treated specimens increased. These results could be attributed to the increase of crystallization with heat-treatment temperature. However, the specific heat capacity of the heat-treated specimens was not affected by the heat-treatment temperature. The thermal conductivities measured from 25℃ to 100℃ were also discussed for application to lighting-emitting diode (LED) packages and substrate materials.

Thermal Stability Evaluation of Diamond-like Carbon for Magnetic Recording Head Application using Raman Spectroscopy

Diamond-like carbon (DLC) films were deposited on magnetic recording heads using filter cathodic arc for improvement of tribological property and corrosion protection. To increase the areal density of magnetic storage, the thickness of DLC film has to be decreased to less than few nanometers. In addition, the heat occurred at the head-disk interface during the operation can impact on the properties and protective performance of DLC films. In this work, the effect of heat on the properties of DLC films was investigated by visible Raman spectroscopy. The Raman spectra of DLC film as a function of heating temperature and time were carried out. The Raman spectra revealed that the degree of graphitization of the DLC films increased with increasing of temperature and time. The relative Raman intensity was found to decrease with possibility of sp3/sp2 ratio decreasing in the films. It can be concluded that the thermal stability of DLC film degraded at high temperature environment.

Electrochemical detection of the thermal stability of n-alkanethiolate monolayers on Au(1 1 1)

The thermal stability of alkanethiolate monolayers of different chain lengths was investigated on Au(1 1 1) by means of electrochemical reductive desorption and AC impedance measurements. The thermal desorption was performed by heating the freshly prepared monolayers between 298 and 573 K in a home-built device under a nitrogen atmosphere. The samples were then transferred to an electrochemical cell and were examined by means of AC impedance spectroscopy and reductive desorption experiments at 298 K. The electrochemical experiments allowed an accurate detection of the coverage of alkanethiolate molecules as a function of heating temperature. The electrochemical detection of the thermal stability allowed us to determine the desorption temperature and the activation energy barrier for the desorption process without the need for ultra-high vacuum (UHV) conditions. The energy barriers for the desorption process are nearly insensitive to the chain length. Density function theory calculations including van der Waals (vdW) interactions were performed to obtain some insights into the nature of the desorption process. We conclude that the monolayer is in a disordered liquid state prior to desorption with most vdW interactions broken.

A comparative study of heat treatment temperature influence on the thickness of zirconia sol–gel thin films by three different techniques: SWE, SEM and AFM

A clear ethanol based precursor sol obtained using zirconium acetate hydroxide was utilized for the deposition of nanometer ZrO2 thin films on 316L stainless steel substrates by a sol–gel dip coating process. The influence of heat treatment temperature on the structural evolution of the films was examined using X-ray diffractometry (XRD) and Fourier transform-infrared spectroscopy (FT-IR). The results indicated that the adopted production route led to the formation of an amorphous structure at 200–300°C and surface tetragonal (t-ZrO2) and monoclinic (m-ZrO2) zirconia phases at 700°C and 900°C temperatures, respectively. Microstructural studies by a scanning electron microscopy (SEM) showed that the morphology and size of the particles of ZrO2 films depend upon the heat treatment temperature. The effect of firing temperature on the thickness of ZrO2 nanometer thin films was studied by three different techniques: single-wavelength ellipsometry (SWE), SEM and atomic force microscopy (AFM). The film thickness measured by the SWE and SEM techniques, as a function of heat treatment temperature, was in close agreement, elucidating a major decrease when heated up to 700°C, and a slight increase between 700 and 900°C. As determined by the AFM studies, the thickness changes were similar to those of SWE and SEM results during the former step, up to 700°C, but it appeared to be constant in the later temperature interval. The AFM profile images showed an increase in surface roughness of the films with rising of the heat treatment temperature.

Effect of Heat Treatment on the Microstructure and Microchemistry of Explosive Welded Joints of Ti-5Ta-1.8Nb and 304L SS

Explosive welding process was used for joining Ti-5Ta-1.8Nb alloy to 304L austenitic stainless steel to avoid the formation of intermetallic phases at the interface which otherwise form in fusion welding processes. Both X-ray diffraction and electron microprobe based analysis showed the absence of intermetallic phases at the weld interface within their detection limits. Strain induced phase transformation due to the deformation induced by explosive welding was observed in both the base materials. The 'as received' explosive joints were further heat treated at 873 and 1073 K for durations in the range of 1 to 20 h to select appropriate temperature for further processing subsequent to welding. Detailed analysis using electron microprobe showed considerable microstructural and micro chemical modification at the weld interface due to inter-diffusion of Fe, Ti, Cr and Ni. The width and number of reaction zones varied as a function of heat treatment temperature and time. From the experiments, it was inferred that even the lowest temperature-time combination, i.e. 873 K-1h, is not suitable for heat treatment of explosive joints of Ti-5Ta-1.8Nb/SS 304L, and further lowering of the process temperature is required.

Effect of Heat Treatment on the Microstructure and Microchemistry of Explosive Welded Joints of Ti-5Ta-1.8Nb and 304L SS

Explosive welding process was used for joining Ti-5Ta-1.8Nb alloy to 304L austenitic stainless steel to avoid the formation of intermetallic phases at the interface which otherwise form in fusion welding processes. Both X-ray diffraction and electron microprobe based analysis showed the absence of intermetallic phases at the weld interface within their detection limits. Strain induced phase transformation due to the deformation induced by explosive welding was observed in both the base materials. The 'as received' explosive joints were further heat treated at 873 and 1073 K for durations in the range of 1 to 20 h to select appropriate temperature for further processing subsequent to welding. Detailed analysis using electron microprobe showed considerable microstructural and micro chemical modification at the weld interface due to inter-diffusion of Fe, Ti, Cr and Ni. The width and number of reaction zones varied as a function of heat treatment temperature and time. From the experiments, it was inferred that even the lowest temperature-time combination, i.e. 873 K-1h, is not suitable for heat treatment of explosive joints of Ti-5Ta-1.8Nb/SS 304L, and further lowering of the process temperature is required.

Investigations on the phase stability of Na +-conducting sodium dysprosium (phospho) silicates

Na +-conducting sodium dysprosium (phospho) silicates with the compositions Na 5DySi 4O 12, Na 3.9Dy 0.6P 0.3Si 2.7O 9 and Na 3.9Dy 0.6Si 3O 8.85 were synthesized by solid state route. The phase evolution in the three systems was studied as a function of heat treatment temperature from 600 °C to 1000 °C by X-ray diffraction technique. It was possible to achieve a NASICON Na 5DySi 4O 12-type single phase with the compositions Na 3.9Dy 0.6P 0.3Si 2.7O 9 and Na 3.9Dy 0.6Si 3O 8.85 at 800 °C. Heat treatment at a higher temperature (>850 °C) resulted in the formation of a less conductive Na 9DySi 6O 18-type phase. Conventional and microwave sintering were carried out on Na 3.9Dy 0.6P 0.3Si 2.7O 9 sample at 800 °C and the ionic conductivities were measured as a function of temperature from 75 °C to 325 °C. The microwave sintered sample exhibited better Na + ionic conductivity of 0.42 × 10 −2 S/cm when compared to that of conventionally sintered sample which was 0.43 × 10 −3 S/cm at 325 °C.

The effect of heating temperature and nitric acid treatments on the performance of Cu- and Zn-based broad spectrum respirator carbons

Impregnated activated carbons (IACs) that are used in broad spectrum gas mask applications have historically contained copper and/or zinc impregnants. The addition of an oxidizing agent, such as nitric acid (HNO 3) can be useful in distributing the metallic impregnants uniformly on the activated carbon substrate. In this work, we study IACs prepared from copper nitrate (Cu(NO 3) 2) and zinc nitrate (Zn(NO 3) 2) precursors as a function of HNO 3 content present in the impregnating solution and as a function of heating temperature. The gas adsorption capacity of the IACs was determined by dynamic flow testing using sulfur dioxide (SO 2), ammonia (NH 3), hydrogen cyanide (HCN) and cyclohexane (C 6H 12) challenge gases under dry and humid conditions. The thermal decomposition and distribution of the impregnant on the activated carbon substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis techniques. Relationships between gas adsorption capacity, impregnant distribution and the species of surface impregnants are discussed.

Wet chemical synthesis and characterization of Na +-conducting sodium dysprosium silicates

The wet chemical synthesis and characterization of the NASICON family series, based on sodium dysprosium (phopho)silicates namely Na 5DySi 4O 12, P doped Na 5DySi 4O 12 (Na 5DyPSi 4O 12), Na 3.9Dy 0.6P 0.3Si 2.7O 9 and Na 4.05Dy 0.55P 0.3Si 2.7O 9, were carried out. Thermal events of the as-dried mixture were analysed by thermogravimetry/differential scanning calorimetry (TG-DSC). Compacted disks of as-dried powder were subjected to conventional heat treatment from 400 to 1000 °C as well as to non-conventional heat treatments like microwave irradiation and spark plasma sintering at various temperatures. The phase evolution was studied as a function of heat treatment temperature by X-ray diffraction. It was found that the Na 5DySi 4O 12 type (N 5) crystal structure that was reported to exhibit high Na +-conductivity could not be achieved using either the conventional or even non-conventional heat-treatment techniques like microwave irradiation and spark plasma sintering, but could be obtained by doping the sodium dysprosium silicate with phosphorous. However, even after doping, the desired N 5 phase was always found to co-exist along with N 9 type (Na 9DySi 6O 18) phase for Na 5DySi 4O 12 and with N 3 type (Na 3DySi 2O 7) phase for Na 3.9Dy 0.6P 0.3Si 2.7O 9 and Na 4.05Dy 0.55P 0.3Si 2.7O 9 compositions up to a heat treatment temperature of 1000 °C.

Influence of thermally induced structural transformations on hardness in Fe 89.8Ni 1.5Si 5.2B 3C 0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe 89.8Ni 1.5Si 5.2B 3C 0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe 2B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe 2B phases of the same composition.

Temperature dependent microstructure of MTES modified hydrophobic silica aerogels

Hydrophobic silica aerogels were prepared using a single step sol–gel process followed by ethanol supercritical drying. Using tetraethoxysilane (TEOS) as a precursor and ammonium hydroxide as a catalyst the aerogel surface was chemically modified with methyltriethoxysilane (MTES). A MTES/TEOS molar ratio of 0.5 (M5) was used. The microstructure of the surface modified aerogels was evaluated as a function of heat treatment temperature over a range of 200–500 °C. The thermal stability was analyzed by simultaneous thermogravimetry and differential scanning calorimetry (TG–DSC) and the microstructure was evaluated by physisorption analysis (BET) and scanning electron microscopy (SEM). The chemical composition and hydrophobicity/hydrophilicity of the aerogels were investigated by Fourier Transform-Infrared (FT-IR) spectroscopy. The M5 aerogels, which were initially hydrophobic, exhibited partial hydrophilicity at treatments above 244.5 °C and complete hydrophilicity above 429.9 °C. The surface area of the aerogels ranged from 776.65–850.20 m 2/g. Pore size increased after heat treatment, ranging from 16.25 to 18.52 nm vs. an initial pore size of 14.71 nm. The maximum pore size of 18.52 nm was found at the lowest heat treatment temperature (~ 200 °C). Heat treatment had a mixed effect on the pore volume, as pore volumes decreased at lower treatments (~ 200–400 °C) and increased at higher heat treatments (~ 450–500 °C) relative to the untreated aerogels. With initial heat treatment the Si–CH 3 group began to oxidize to Si-OH. Aerogels heated above 429.9 °C exhibited hydroxyl polymerization leading to aerogels with large particles and a dense microstructure.

Nanostructural development of non-graphitising carbons probed using TEM/EELS: The importance of fullerenes?

This work presents a comprehensive study of a set of non-graphitising carbons as a function of heat treatment temperature (HTT) up to 3000 °C using a combination of density measurements, X-ray and electron diffraction, high resolution TEM and low loss and core loss EELS. Results are compared to those obtained from graphitising carbons. Of interest is the variation in plasmon energy with HTT and its relationship to density as well as the ratio of sp2to sp3 bonded carbon species derived from the C K-edge using a revised analytical procedure. Results are reviewed in light of the fairly recent suggestion that the intrinsic structure of non-graphitising carbons is based on the inclusion of fullerene-like units. We speculate as to whether this might have a broader significance for carbonaceous materials in general.

Conductivity and polarization of carbonaceous nanotubes derived from polyaniline nanotubes and their electrorheology when dispersed in silicone oil

Nitrogen-enriched carbonaceous nanotubes (N-CTs) were prepared by the heat treatment of conducting polyaniline (PANI) nanotubes and then were used as new carbonaceous electrorheological (ER) fluids. Characterization showed that the nanotubular morphology of the original PANI was preserved after heat treatment, whereas the chemical structure and conductivity were changed significantly depending on the heat treatment temperatures. Under electric fields, the rheological properties of the N-CT suspensions prepared by the ultrasonic dispersion of the N-CTs in silicone oil were measured. This showed that the N-CT suspensions possessed versatile ER performance including high ER efficiency, good dispersion stability, and temperature stability. Especially, compared to the corresponding heat treated granular PANI suspensions, the N-CT suspensions showed better dispersion stability and higher ER effect. Furthermore, the ER effect of N-CT suspensions could be adjusted by varying heat treatment temperatures and the N-CTs obtained at around 600°C exhibited the maximum ER effect. This could be explained by the polarization response, which originated from the regular change of conductivity of N-CTs as a function of heat treatment temperatures.

Critical crack size of healing possibility of SiC ceramics

Crack-healing behavior of SiC ceramics with additive SiO 2 has been studied as functions of heat-treatment temperature and crack size. Results showed that heat treatment in air could significantly increase the strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature had 1 h at an atmospheric level of 1373 K. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to 450 μm. The long crack up to 1000 μm with width 1.4 μm could completely heal the surface crack.

Rheology and Oxidative Stability of Whey Protein Isolate‐Stabilized Menhaden Oil‐in‐Water Emulsions as a Function of Heat Treatment

Menhaden oil-in-water emulsions (20%, v/v) were stabilized by 2 wt% whey protein isolate (WPI) with 0.2 wt% xanthan gum (XG) in the presence of 10 mM CaCl(2) and 200 microM EDTA at pH 7. Droplet size, lipid oxidation, and rheological properties of the emulsions were investigated as a function of heating temperature and time. During heating, droplet size reached a maximum at 70 degrees C and then decreased at 90 degrees C, which can be attributed to both heating effect on increased hydrophobic attractions and the influence of CaCl(2) on decreased electrostatic repulsions. Combination of effects of EDTA and heat treatment contributed to oxidative stability of the heated emulsions. The rheological data indicate that the WPI/XG-stabilized emulsions undergo a state transition from being viscous like to an elastic like upon substantial thermal treatment. Heating below 70 degrees C or for less than 10 min at 70 degrees C favors droplet aggregation while heating at 90 degrees C or for 15 min or longer at 70 degrees C facilitates WPI adsorption and rearrangement. WPI adsorption leads to the formation of protein network around the droplet surface, which promotes oxidative stability of menhaden oil. Heating also aggravates thermodynamic incompatibility between XG and WPI, which contributes to droplet aggregation and the accumulation of more WPI around the droplet surfaces as well.